This invention relates to a cruise control apparatus for an automobile, and more particularly to a compact cruise control apparatus with a motorized actuator.
A cruise control apparatus is a device for maintaining the speed of an automobile at a constant level without the driver having to depress the accelerator pedal. In one type of cruise control apparatus, the speed is controlled by a motorized actuator which adjusts the degree of opening of the throttle valve of the engine of the automobile.
FIG. 1 schematically illustrates a conventional cruise control apparatus of this type. The cruise control apparatus has a motorized actuator 1 which includes an unillustrated control motor such as a polyphase step motor. The control motor has an output shaft on which a wire take-up reel 2 is mounted. A connecting wire 3a has one end wrapped around the take-up reel 2 and the other end secured to one end of a throttle link 5a. The other end of the throttle link 5a is connected to a throttle valve 6 which is pivotably mounted in the barrel 7 of the carburetor of the engine of the automobile. The carburetor barrel 7 communicates with the body 9 of the engine via an intake manifold 8. When the control motor of the actuator is rotated, the connecting wire 3a is reeled in or out, thereby opening or closing the throttle valve 6. An accelerator pedal 4 is also connected to the throttle valve 6 through a connecting wire 3b and a throttle link 5b. With this structure, the degree of opening of the throttle valve 6 can be adjusted either by the rotation of the wire take-up reel 2 by the actuator 1 or by the depression of the accelerator pedal 4 by the driver of the automobile.
The operation of the motorized actuator 1 is controlled by a control unit 11 which is responsive to input signals from a speedometer 10 and a control panel 12 into which the driver inputs a desired speed. The control unit 11 sends command signals to the actuator 1, which adjusts the degree of opening of the throttle valve 6 so that the actual speed of the automobile, as indicated by the input signal from the speedometer 10, is maintained at a desired speed, as indicated by the input signal from the control panel 12.
In a conventional cruise control apparatus for this type, the control unit 11 and the actuator 1 which it controls are separate units which are connected by external electrical wiring. From the standpoint of decreasing electrical noise, it is desirable that the length of wiring between the two be as short as possible. Another reason that the wiring should be short is that the longer the electrical wiring, the more electrical connectors are necessary, and the greater is the possibility of poor electrical connections. However, because of the physical size of the units, it is not always possible to dispose them in close proximity with one another. Therefore, the amount of wiring connecting the two may be undesirably long, resulting in a large amount of electrical noise.
Furthermore, the control unit 11 includes drivers for the motor of the actuator 1. As these drivers generate heat, the control unit 11 must include a heat sink or other means for dissipating the heat from the drivers. This increases the size of the control unit 11 and imposes limitations on the locations in which it can be installed.
In addition, the control accuracy of the control unit 11 is determined by the total of the dispersion among all the elements. Generally, representative values of the gain of the vehicle and the gain of the actuator 1 are used, and the apparatus is adjusted to have an average gain value which is relatively in agreement with the representative values. As a result, due to dispersion among vehicles and actuators, when the apparatus is mounted in a vehicle, combinations inevitably result which cause functional problems.